1. Field of the Invention
The present invention relates to a CRT device comprising a cold cathode electron gun, particularly to a technique to improve resolution of the CRT device.
2. Description of the Related Art
In recent years, there has been development in CRT devices comprising an electron gun in which a cold cathode is applied instead of a thermal cathode. Since a cold cathode electron gun does not need a heater, the power consumption is small. Also, since the electron gun does not suffer from “doming” which is caused by heat, the possibility of having a deviation in positions of the electron beams is lower.
Although the cold cathode has such an advantage, it is difficult to converge the electron beam emitted from a field emitter array of a cold cathode electron gun, because the initial speed is high, and also the exit angle is large. Thus, the diameter of a spot formed on the phosphor screen of the CRT device (hereafter, referred to as “spot diameter”) gets large, and high enough resolution is not yet achieved.
In order to cope with such a problem, proposed is a cathode ray tube that is disclosed in the Japanese Unexamined Patent Application Publication No. 8-106848, for instance. This cathode ray tube takes the aforementioned technical common sense into consideration, and improves resolution, with use of the dual gate method, by converging electron beams on the phosphor screen without forming a crossover point.
More specifically, the FEA (Field Emitter Array) according to the dual gate method comprised in such a cathode ray tube is a semiconductor element in which two gate electrodes are stacked up in the tube axis direction. An electron beam is emitted from an emitter electrode by an electric field formed by the first gate electrode provided closer to the emitter electrode, and an adjustment is made on the spot diameter by reducing the beam diameter of the electron beam with the electric field formed by the second gate electrode that has a lower voltage than the first gate electrode.
Such a cathode ray tube however presents a problem that the expected function cannot be rendered because the electric fields formed by those two gate electrodes influence each other, when the distance between the first gate electrode and the second gate electrode is short.
On the other hand, in order to make the distance between those two gate electrodes long, it is necessary to make the thickness of the insulating layer between the gate electrodes large; however, making the insulating layer thicker is difficult in terms of the semiconductor process technique, and the Field Emitter Array according to the dual gate method has low feasibility at the moment.